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Ron Smith answers questions about flowers, trees, gardens and shrubs.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have dieffenbachia plants that are very healthy. However, I can’t keep them growing upright. They start to get top-heavy and then bend and curl. The parts that grow from the stumps after making a cutting seem the most susceptible. My place only gets sun from one direction. I should add that these plants are descendants of a plant my uncle bought for my aunt 55 years ago. (e-mail reference)

A: Research three to four decades ago found that houseplants that were not subjected to forced movement from a breeze or other mechanical means grew fast but were weak and spindly. The majestic plants that one sees indoors are getting movement from fans that build “stress cells.” I would suggest that you take a cutting again, but this time put a circulating fan in operation for about 12 hours a day as it grows. Supplement it with extra light if necessary.

Q: I have had spider plants for decades. In the last 18 months, something strange has been happening to the plants. One by one, the lower leaves are rotting from the inside. This goes on until the plant dies. The roots seem fine. While the leaves are browning, there is new growth and the rest of the plant seems fine. It started with one plant and gradually spread from room to room. At the moment, only the bathroom plant seems OK. I tried baby plantlets, but the same thing happened. I will be extremely grateful for any light you can shed on this problem. (United Kingdom)

A: This sounds like the soil or media has some kind of fungal pathogen in it. Are you using sterilized or pasteurized media in growing these plants? I would suggest repotting any surviving plants in new or well-cleaned containers. Use a soil media that is known to be pasteurized or sterilized. Be sure to cut off anything that appears to be dead or decaying.

Q: We have been having troubles with a worm that burrows through the stem of our vine plants about 2 inches above ground. The worm leaves a visible hole, especially on our winter squash. It killed our cucumbers and summer squash plants. I found one in the stem of a buttercup squash last fall. It was about 1 to 1 1/4 inches long and about the thickness of an earthworm. It had an off-white color. They seem to start doing their damage after the first of August. We do use Sevin to control the cucumber beetles, but it doesn't seem to affect this worm. Is there anything we could use at planting time, such as a seed or ground treatment? How about controlling it during the growing season? (e-mail reference)

A: This is squash vine borer causing your problem. It is an especially nasty pest because the borer, a grubby white caterpillar, hides inside the hollow vines of popular squash family plants, such as pumpkins and zucchini, as it does its dirty work. Gardeners generally don’t notice anything wrong until the whole plant starts wilting. By then, it’s too late to save the plant. The trick will be to focus on prevention. The problem begins in late spring when a moth lays its eggs at the base of your squash plants. Each female will lay about 200 eggs. The eggs are so small they are almost impossible to spot. The eggs hatch in a week or two. The grubs that emerge quickly tunnel into the hollow plant stems the eggs were attached to. These hungry youngsters feed, hidden from view, for a month or so and then drop down into the soil to pupate. Rotate your planting of squash, cucumbers and pumpkins with a crop that is entirely different, such as beans, corn or tomatoes. Floating row covers will help prevent the moth from getting to the squash plants. If you keep them covered until the first of July, all the egg laying activity should be finished and you can remove the covers. You could use a material, such as Dipel, which is an organic control that will stop the critter from eating too much of the vine before it expires. Whatever you do, don't use the floating row cover technique where you had squash vine borer activity the year before! If you do that, the adult females will be in squash heaven because they will be protected from the elements. Depending on your powers of observation, you may have some success with deworming the vines. At the first signs of the sawdustlike frass, slit the vines lengthwise near where the damage is found and remove the borers. The stems should be covered immediately with soil. Sanitation also is important. After harvest is complete, the vines should be removed from the garden and composted to prevent the remaining borers from completing larval development. Burying a few nodes along each vine will encourage rooting at these nodes. This will lessen the impact if squash vine borers girdle the base of the vine.

Q: Your answer to one of my e-mails about starting seeds indoors said to always use a pasteurized media. What exactly is that? Also, what is your opinion of pellet greenhouse kits? (West Fargo, N.D.)

A: Most potting soil or seed-starting media that you purchase in a garden center is pasteurized and contains inert material, such as vermiculite or perlite, which is sterile. I have nothing against pellet greenhouse kits for homeowners to use in getting things up and growing. If this is something that teases your interest, go for it!

Q: I can’t grow tomatoes! About 10 years ago, I bought three acres of land and planted about 180 trees on the property. About 30 trees are black walnut. I think that’s my problem. I read in one of your articles about that problem. I always could grow good tomatoes in town but not out in the country. Is there anything I can do? Last year, I tried earth boxes as far away from the trees as I could, but still no tomatoes. If I do get tomatoes, it’s really late in the season. (Redfield, S.D.)

A: Tomatoes and other members of this family are severely affected by the exudates from black walnut trees. It migrates from the leaves and root system. Once in the soil, it will have an impact for years. I'm not sure what you mean by earth boxes. If the boxes are filled with potting soil and not native soil, then I don't see why the boxes wouldn’t support tomato growth and fruit production. Try changing to varieties such as early girl, early wonder or celebrity. The first two are early season and taste great. Celebrity is a midseason variety and a former All-America selection. As long as tomatoes get full sun, are not near walnut trees and have ample water and nutrients, they should be very productive for you.

Q: I want to transplant some eastern red cedar trees. My wife keeps reminding me about an old wives’ tale that says if one plants a cedar tree that one will die when that tree gets big enough to shade a grave. What do you think? Any truth to that old wives’ tale or is she just being superstitious? (Tennessee)

A: Since there is a great enough distance between North Dakota and Tennessee, I don't have to worry about getting assaulted by your wife for my answer. She is wrong. Whether or not you want to tell her she is being silly or superstitious is your liability! Thanks for a very unique question.

Q: Can you recommend a different variety of tree that is similar in leaf shape and bark to patmore and green ash trees? (e-mail reference)

A: I can give you a list of trees with pinnately compounded leaves, which is about the only characteristic that would be consistent. Since you didn't tell me where it is you live, check with local authorities to be sure the one you are interested in isn't considered invasive in your part of the country. The tree list includes amur cork, honey locust, black locust, box elder maple and black walnut.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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